Embodiments of the invention relate generally to sensors that may be used to provide position/orientation information for an instrument, implant, or device used in a medical context, such as in a surgical or interventional context, and, in particular, to multi-axis packaged magneto-resistance sensors.
In various medical contexts it may be desirable to acquire position and/or orientation information for a medical instrument, implant, or device that is navigated or positioned (externally or internally) relative to a patient. For example, in surgical and/or interventional contexts, it may be useful to acquire position and/or orientation information for a medical device, or portion of a medical device, even when the device or relevant portion is otherwise out of view, such as within a patient's body. Likewise, in certain procedures where an imaging technique is used to observe all or part of the position and orientation information, it may be useful to have position and orientation information derived from the tracked device itself that can be related to other data, such as image data that may be contemporaneously acquired.
In such medical contexts, electromagnetic (EM) sensors may be implemented to provide the position/orientation information for the medical instrument, implant, or device. The EM sensors may be utilized as part of a position/orientation tracking system that includes a controller, a magnetic field source transmitter that generates a magnetic field with spatially varying characteristics (so the field is different at different locations), and an EM sensor that is integrated with the medical instrument, implant or device being tracked. The position of the EM sensor may be determined by calculating the position where the EM sensor observations agree with the calculated magnetic field from the transmitter—i.e., by measuring the mutual inductance between the transmitter and the EM sensor and processing the measured values to resolve a position and orientation of the EM sensor relative to the transmitter.
One issue that can arise with respect to navigation sensors suitable for acquiring position and orientation information in this manner is the size of the position and orientation sensor relative to the device that is to be tracked. In particular, in surgical and interventional contexts, it may be desired to use an instrument, implant or device that is as small as possible, either due to the size and/or fragility of the anatomy undergoing the procedure or to otherwise minimize the trauma associated with the procedure. Therefore, it may also be desirable to use a navigation sensor that is suitably sized for the instruments, implants or devices being employed. However, it may be difficult to construct a suitable position and orientation sensor assembly that provides the desired position and orientation information with the desired precision and accuracy and which is of a suitable size for use with or within the instruments, implants or devices in question. For example, existing position and orientation sensor assemblies may often be structured as a single chip containing two orthogonally placed sense circuits, a calibration coil, and an initialization coil, with such assemblies being approximately 1 mm2 in size. While this size position and orientation sensor assembly is useable in many applications in the neural, cardiac, and orthopedic spaces, it cannot be integrated into many standard catheter lumens and needles that are smaller than 1 mm.
Therefore, it is desirable to provide a position and orientation sensor assembly whose size is reduced as compared to existing position and orientation sensor assembly options. It is further desirable that such a position and orientation sensor assembly would still provide position and orientation information with adequate precision and accuracy and with sensing in six degrees of freedom.